1
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Jung DM, Kwon E, Choi S, Kim KK. 1,2,4-trihydroxybenzene induces stress granule formation and causes DNA damage in human keratinocytes. Toxicol In Vitro 2023; 92:105638. [PMID: 37406782 DOI: 10.1016/j.tiv.2023.105638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 04/26/2023] [Accepted: 06/29/2023] [Indexed: 07/07/2023]
Abstract
Household chemical products are typically evaluated for toxicity through ingestion and inhalation, with limited information on skin absorption. Furthermore, current research focuses on the long-term toxic effects of harmful substances contained in these household chemical products, however not much is known about their acute toxic effects. In this study, the effects of 1,2,4-trihydroxybenzene (THB) in human keratinocytes by examining its effects on stress granule (SG) formation, a marker of acute stress response, and DNA double strand breaks caused by repeated exposure. THB effectively induced SG formation via endoplasmic reticulum stress-mediated eIF2α phosphorylation in keratinocytes. Furthermore, repeated exposure to THB causes apoptotic cell death due to DNA double strand breaks. Collectively, THB exposure leads to skin toxicity, suggesting precautions for the use of THB-containing household chemical products.
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Affiliation(s)
- Da-Min Jung
- Department of Biochemistry, College of Natural Sciences, Chungnam National University, Daejeon 34134, Republic of Korea
| | - Eunhye Kwon
- Department of Biochemistry, College of Natural Sciences, Chungnam National University, Daejeon 34134, Republic of Korea
| | - Sunkyung Choi
- Department of Biochemistry, College of Natural Sciences, Chungnam National University, Daejeon 34134, Republic of Korea.
| | - Kee K Kim
- Department of Biochemistry, College of Natural Sciences, Chungnam National University, Daejeon 34134, Republic of Korea.
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2
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Lines CL, McGrath MJ, Dorwart T, Conn CS. The integrated stress response in cancer progression: a force for plasticity and resistance. Front Oncol 2023; 13:1206561. [PMID: 37601686 PMCID: PMC10435748 DOI: 10.3389/fonc.2023.1206561] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Accepted: 06/07/2023] [Indexed: 08/22/2023] Open
Abstract
During their quest for growth, adaptation, and survival, cancer cells create a favorable environment through the manipulation of normal cellular mechanisms. They increase anabolic processes, including protein synthesis, to facilitate uncontrolled proliferation and deplete the tumor microenvironment of resources. As a dynamic adaptation to the self-imposed oncogenic stress, cancer cells promptly hijack translational control to alter gene expression. Rewiring the cellular proteome shifts the phenotypic balance between growth and adaptation to promote therapeutic resistance and cancer cell survival. The integrated stress response (ISR) is a key translational program activated by oncogenic stress that is utilized to fine-tune protein synthesis and adjust to environmental barriers. Here, we focus on the role of ISR signaling for driving cancer progression. We highlight mechanisms of regulation for distinct mRNA translation downstream of the ISR, expand on oncogenic signaling utilizing the ISR in response to environmental stresses, and pinpoint the impact this has for cancer cell plasticity during resistance to therapy. There is an ongoing need for innovative drug targets in cancer treatment, and modulating ISR activity may provide a unique avenue for clinical benefit.
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Affiliation(s)
| | | | | | - Crystal S. Conn
- Department of Radiation Oncology, University of Pennsylvania, Perelman School of Medicine, Philadelphia, PA, United States
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3
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Eif2s3y Promotes the Proliferation of Spermatogonial Stem Cells by Activating ERK Signaling. Stem Cells Int 2021; 2021:6668658. [PMID: 33603791 PMCID: PMC7869416 DOI: 10.1155/2021/6668658] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Revised: 01/09/2021] [Accepted: 01/12/2021] [Indexed: 01/15/2023] Open
Abstract
The future fertility of males with cancer may be irreversibly compromised by chemotherapy and/or radiotherapy. Spermatogonial stem cell transplantation is believed to be a way to restore fertility in men. However, the survival efficiency of transplanted cells is still low. Eukaryotic translation initiation factor 2 subunit 3 and structural gene Y-linked (Eif2s3y) located on the Y chromosome of male animals is a coding gene of eIF2γ which mainly functions in translation initiation. Recently, the emerging role of Eif2s3y in spermatogenesis has been emphasized in several studies. However, the underlying mechanism is still unclear. In addition, how Eif2s3y functions in large animals remains largely unknown. In this study, we obtained the CDS sequence of the Eif2s3y gene from the testis of dairy goats and found that this gene was highly expressed in the testis and was evolutionarily conserved among different species. Interestingly, overexpression of Eif2s3y promoted the proliferation of spermatogonial stem cells of dairy goats by activating the ERK signaling pathway. In animal experiments, overexpressing Eif2s3y promoted transplanted goat spermatogonial stem cells and produced more colonies after microinjection into the seminiferous tubules of infertile mice. In conclusion, our study highlights an undiscovered role of Eif2s3y in dairy goat reproduction. This finding may provide an important basis for future works regarding male spermatogenic cell restoration and represent a major advance toward surrogate sires becoming a tool for disseminating and regenerating germplasm in all mammals.
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4
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Kotzaeridou U, Young-Baird SK, Suckow V, Thornburg AG, Wagner M, Harting I, Christ S, Strom T, Dever TE, Kalscheuer VM. Novel pathogenic EIF2S3 missense variants causing clinically variable MEHMO syndrome with impaired eIF2γ translational function, and literature review. Clin Genet 2020; 98:507-514. [PMID: 32799315 DOI: 10.1111/cge.13831] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 08/08/2020] [Accepted: 08/13/2020] [Indexed: 12/12/2022]
Abstract
Rare pathogenic EIF2S3 missense and terminal deletion variants cause the X-linked intellectual disability (ID) syndrome MEHMO, or a milder phenotype including pancreatic dysfunction and hypopituitarism. We present two unrelated male patients who carry novel EIF2S3 pathogenic missense variants (p.(Thr144Ile) and p.(Ile159Leu)) thereby broadening the limited genetic spectrum and underscoring clinically variable expressivity of MEHMO. While the affected male with p.(Thr144Ile) presented with severe motor delay, severe microcephaly, moderate ID, epileptic seizures responsive to treatments, hypogenitalism, central obesity, facial features, and diabetes, the affected male with p.(Ile159Leu) presented with moderate ID, mild motor delay, microcephaly, epileptic seizures resistant to treatment, central obesity, and mild facial features. Both variants are located in the highly conserved guanine nucleotide binding domain of the EIF2S3 encoded eIF2γ subunit of the heterotrimeric translation initiation factor 2 (eIF2) complex. Further, we investigated both variants in a structural model and in yeast. The reduced growth rates and lowered fidelity of translation with increased initiation at non-AUG codons observed for both mutants in these studies strongly support pathogenicity of the variants.
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Affiliation(s)
- Urania Kotzaeridou
- Division of Child Neurology and Inherited Metabolic Diseases, Centre for Paediatrics and Adolescent Medicine, University Hospital Heidelberg, Heidelberg, Germany
| | - Sara K Young-Baird
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, Maryland, USA.,National Institute of General Medical Sciences, NIH, Bethesda, Maryland, USA
| | - Vanessa Suckow
- Research Group Development and Disease, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - Alexis G Thornburg
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, Maryland, USA
| | - Matias Wagner
- Institute of Human Genetics, Technical University München, Munich, Germany.,Institute of Human Genetics, Helmholtz Zentrum München, Neuherberg, Germany.,Institute for Neurogenomics, Helmholtz Zentrum München, Neuherberg, Germany
| | - Inga Harting
- Department of Neuroradiology, University Hospital Heidelberg, Heidelberg, Germany
| | - Stine Christ
- Division of Child Neurology and Inherited Metabolic Diseases, Centre for Paediatrics and Adolescent Medicine, University Hospital Heidelberg, Heidelberg, Germany
| | - Tim Strom
- Institute of Human Genetics, Technical University München, Munich, Germany
| | - Thomas E Dever
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, Maryland, USA
| | - Vera M Kalscheuer
- Research Group Development and Disease, Max Planck Institute for Molecular Genetics, Berlin, Germany
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5
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Kim MH, Kim S. Structures and functions of multi-tRNA synthetase complexes. Enzymes 2020; 48:149-173. [PMID: 33837703 DOI: 10.1016/bs.enz.2020.06.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/23/2023]
Abstract
Human body is a finely-tuned machine that requires homeostatic balance based on systemically controlled biological processes involving DNA replication, transcription, translation, and energy metabolism. Ubiquitously expressed aminoacyl-tRNA synthetases have been investigated for many decades, and they act as cross-over mediators of important biological processes. In particular, a cytoplasmic multi-tRNA synthetase complex (MSC) appears to be a central machinery controlling the complexity of biological systems. The structural integrity of MSC determined by the associated components is correlated with increasing biological complexity that links to system development in higher organisms. Although the role of the MSCs is still unclear, this chapter describes the current knowledge on MSC components that are associated with and regulate functions beyond their catalytic activities with focus on human MSC.
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Affiliation(s)
- Myung Hee Kim
- Infection and Immunity Research Laboratory, Metabolic Regulation Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon, South Korea.
| | - Sunghoon Kim
- Medicinal Bioconvergence Research Center, College of Pharmacy & School of Medicine, Yonsei University, Incheon, South Korea.
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6
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Vincent HA, Ziehr B, Lenarcic EM, Moorman NJ. Human cytomegalovirus pTRS1 stimulates cap-independent translation. Virology 2019; 537:246-253. [PMID: 31539772 PMCID: PMC8281606 DOI: 10.1016/j.virol.2019.08.026] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 08/28/2019] [Accepted: 08/28/2019] [Indexed: 01/08/2023]
Abstract
Human cytomegalovirus (HCMV) manipulates multiple cellular processes to facilitate virus replication, including the control of mRNA translation. We previously showed that the HCMV TRS1 protein (pTRS1) promotes cap-dependent mRNA translation independent of its ability to antagonize the antiviral protein PKR. Here we find that pTRS1 enhances internal ribosome entry site (IRES) activity using a novel circular RNA reporter that lacks an mRNA cap and poly(A) tail. Additionally, pTRS1 expression increases the activity of cellular IRESs that control the expression of proteins needed for efficient HCMV replication. We find that the ability of pTRS1 to enhance cap-independent translation is separable from its ability to antagonize PKR, but requires the pTRS1 RNA binding domain. Together these data show that pTRS1 stimulates cap-independent translation and suggest a role for pTRS1 in alternative translation initiation pathways during HCMV infection.
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Affiliation(s)
- Heather A Vincent
- Department of Microbiology & Immunology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Benjamin Ziehr
- Department of Microbiology & Immunology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Erik M Lenarcic
- Department of Microbiology & Immunology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Nathaniel J Moorman
- Department of Microbiology & Immunology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
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7
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Start Codon Recognition in Eukaryotic and Archaeal Translation Initiation: A Common Structural Core. Int J Mol Sci 2019; 20:ijms20040939. [PMID: 30795538 PMCID: PMC6412873 DOI: 10.3390/ijms20040939] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Revised: 02/11/2019] [Accepted: 02/13/2019] [Indexed: 01/12/2023] Open
Abstract
Understanding molecular mechanisms of ribosomal translation sheds light on the emergence and evolution of protein synthesis in the three domains of life. Universally, ribosomal translation is described in three steps: initiation, elongation and termination. During initiation, a macromolecular complex assembled around the small ribosomal subunit selects the start codon on the mRNA and defines the open reading frame. In this review, we focus on the comparison of start codon selection mechanisms in eukaryotes and archaea. Eukaryotic translation initiation is a very complicated process, involving many initiation factors. The most widespread mechanism for the discovery of the start codon is the scanning of the mRNA by a pre-initiation complex until the first AUG codon in a correct context is found. In archaea, long-range scanning does not occur because of the presence of Shine-Dalgarno (SD) sequences or of short 5′ untranslated regions. However, archaeal and eukaryotic translation initiations have three initiation factors in common: e/aIF1, e/aIF1A and e/aIF2 are directly involved in the selection of the start codon. Therefore, the idea that these archaeal and eukaryotic factors fulfill similar functions within a common structural ribosomal core complex has emerged. A divergence between eukaryotic and archaeal factors allowed for the adaptation to the long-range scanning process versus the SD mediated prepositioning of the ribosome.
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8
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Merrick WC, Pavitt GD. Protein Synthesis Initiation in Eukaryotic Cells. Cold Spring Harb Perspect Biol 2018; 10:cshperspect.a033092. [PMID: 29735639 DOI: 10.1101/cshperspect.a033092] [Citation(s) in RCA: 197] [Impact Index Per Article: 32.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
This review summarizes our current understanding of the major pathway for the initiation phase of protein synthesis in eukaryotic cells, with a focus on recent advances. We describe the major scanning or messenger RNA (mRNA) m7G cap-dependent mechanism, which is a highly coordinated and stepwise regulated process that requires the combined action of at least 12 distinct translation factors with initiator transfer RNA (tRNA), ribosomes, and mRNAs. We limit our review to studies involving either mammalian or budding yeast cells and factors, as these represent the two best-studied experimental systems, and only include a reference to other organisms where particular insight has been gained. We close with a brief description of what we feel are some of the major unknowns in eukaryotic initiation.
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Affiliation(s)
- William C Merrick
- Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
| | - Graham D Pavitt
- Division of Molecular and Cellular Function, Faculty of Biology Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester M13 9PT, United Kingdom
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9
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Chang YH, Nishimura S, Oishi H, Kelly VP, Kuno A, Takahashi S. TRMT2A is a novel cell cycle regulator that suppresses cell proliferation. Biochem Biophys Res Commun 2018; 508:410-415. [PMID: 30502085 DOI: 10.1016/j.bbrc.2018.11.104] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Accepted: 11/16/2018] [Indexed: 01/15/2023]
Abstract
During the maturation of transfer RNA (tRNA), a variety of chemical modifications can be introduced at specific nucleotide positions post-transcriptionally. 5-Methyluridine (m5U) is one of the most common and conserved modifications from eubacteria to eukaryotes. Although TrmA protein in Escherichia coli and Trm2p protein in Saccharomyces cerevisiae, which are responsible for the 5-methylation of uracil at position 54 (m5U54) on tRNA, are well characterized, the biological function of the U54 methylation responsible enzyme in mammalian species remains largely unexplored. Here, we show that the mammalian tRNA methyltransferase 2 homolog A (TRMT2A) protein harbors an RNA recognition motif in the N-terminus and the conserved uracil-C5-methyltransferase domain of the TrmA family in the C-terminus. TRMT2A predominantly localizes to the nucleus in HeLa cells. TRMT2A-overexpressing cells display decreased cell proliferation and altered DNA content, while TRMT2A-deficient cells exhibit increased growth. Thus, our results reveal the inhibitory role of TRMT2A on cell proliferation and cell cycle control, providing evidence that TRMT2A is a candidate cell cycle regulator in mammals.
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Affiliation(s)
- Yu-Hsin Chang
- Department of Anatomy and Embryology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan; Ph.D. Program in Human Biology, School of Integrative and Global Majors, University of Tsukuba, Ibaraki, Japan
| | - Susumu Nishimura
- Laboratory Animal Resource Center, University of Tsukuba, Ibaraki, Japan
| | - Hisashi Oishi
- Department of Comparative and Experimental Medicine, Nagoya City University Graduate School of Medical Sciences, Aichi, Japan
| | - Vincent P Kelly
- School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute (TBSI), Trinity College Dublin, Ireland
| | - Akihiro Kuno
- Department of Anatomy and Embryology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
| | - Satoru Takahashi
- Department of Anatomy and Embryology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan; Laboratory Animal Resource Center, University of Tsukuba, Ibaraki, Japan; Life Science Center, Tsukuba Advanced Research Alliance (TARA), University of Tsukuba, Ibaraki, Japan; International Institute for Integrative Sleep Medicine (WPI-IIIS), University of Tsukuba, Ibaraki, Japan; Transborder Medical Research Center, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
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10
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Hashem Y, Frank J. The Jigsaw Puzzle of mRNA Translation Initiation in Eukaryotes: A Decade of Structures Unraveling the Mechanics of the Process. Annu Rev Biophys 2018; 47:125-151. [PMID: 29494255 DOI: 10.1146/annurev-biophys-070816-034034] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Translation initiation in eukaryotes is a highly regulated and rate-limiting process. It results in the assembly and disassembly of numerous transient and intermediate complexes involving over a dozen eukaryotic initiation factors (eIFs). This process culminates in the accommodation of a start codon marking the beginning of an open reading frame at the appropriate ribosomal site. Although this process has been extensively studied by hundreds of groups for nearly half a century, it has been only recently, especially during the last decade, that we have gained deeper insight into the mechanics of the eukaryotic translation initiation process. This advance in knowledge is due in part to the contributions of structural biology, which have shed light on the molecular mechanics underlying the different functions of various eukaryotic initiation factors. In this review, we focus exclusively on the contribution of structural biology to the understanding of the eukaryotic initiation process, a long-standing jigsaw puzzle that is just starting to yield the bigger picture.
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Affiliation(s)
- Yaser Hashem
- INSERM U1212, Institut Européen de Chimie et Biologie, Université de Bordeaux, Pessac 33607, France;
| | - Joachim Frank
- Department of Biological Sciences, Columbia University, New York, NY 10032, USA;
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11
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Hinnebusch AG. Structural Insights into the Mechanism of Scanning and Start Codon Recognition in Eukaryotic Translation Initiation. Trends Biochem Sci 2017; 42:589-611. [PMID: 28442192 DOI: 10.1016/j.tibs.2017.03.004] [Citation(s) in RCA: 199] [Impact Index Per Article: 28.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2017] [Revised: 03/12/2017] [Accepted: 03/20/2017] [Indexed: 12/21/2022]
Abstract
Initiation of translation on eukaryotic mRNAs generally follows the scanning mechanism, wherein a preinitiation complex (PIC) assembled on the small (40S) ribosomal subunit and containing initiator methionyl tRNAi (Met-tRNAi) scans the mRNA leader for an AUG codon. In a current model, the scanning PIC adopts an open conformation and rearranges to a closed state, with fully accommodated Met-tRNAi, upon AUG recognition. Evidence from recent high-resolution structures of PICs assembled with different ligands supports this model and illuminates the molecular functions of eukaryotic initiation factors eIF1, eIF1A, and eIF2 in restricting to AUG codons the transition to the closed conformation. They also reveal that the eIF3 complex interacts with multiple functional sites in the PIC, rationalizing its participation in numerous steps of initiation.
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Affiliation(s)
- Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
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12
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Mechanism and Regulation of Protein Synthesis in Saccharomyces cerevisiae. Genetics 2017; 203:65-107. [PMID: 27183566 DOI: 10.1534/genetics.115.186221] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 02/24/2016] [Indexed: 12/18/2022] Open
Abstract
In this review, we provide an overview of protein synthesis in the yeast Saccharomyces cerevisiae The mechanism of protein synthesis is well conserved between yeast and other eukaryotes, and molecular genetic studies in budding yeast have provided critical insights into the fundamental process of translation as well as its regulation. The review focuses on the initiation and elongation phases of protein synthesis with descriptions of the roles of translation initiation and elongation factors that assist the ribosome in binding the messenger RNA (mRNA), selecting the start codon, and synthesizing the polypeptide. We also examine mechanisms of translational control highlighting the mRNA cap-binding proteins and the regulation of GCN4 and CPA1 mRNAs.
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13
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Jinno D, Kanemitsu Y, Saitoh K, Nankumo S, Tsukamoto H, Matsumoto Y, Abe T, Tomioka Y. Rapid and selective simultaneous quantitative analysis of modified nucleosides using multi-column liquid chromatography-tandem mass spectrometry. J Anal Sci Technol 2017. [DOI: 10.1186/s40543-017-0110-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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14
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Cryo-EM study of start codon selection during archaeal translation initiation. Nat Commun 2016; 7:13366. [PMID: 27819266 PMCID: PMC5103072 DOI: 10.1038/ncomms13366] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Accepted: 09/27/2016] [Indexed: 11/18/2022] Open
Abstract
Eukaryotic and archaeal translation initiation complexes have a common structural core comprising e/aIF1, e/aIF1A, the ternary complex (TC, e/aIF2-GTP-Met-tRNAiMet) and mRNA bound to the small ribosomal subunit. e/aIF2 plays a crucial role in this process but how this factor controls start codon selection remains unclear. Here, we present cryo-EM structures of the full archaeal 30S initiation complex showing two conformational states of the TC. In the first state, the TC is bound to the ribosome in a relaxed conformation with the tRNA oriented out of the P site. In the second state, the tRNA is accommodated within the peptidyl (P) site and the TC becomes constrained. This constraint is compensated by codon/anticodon base pairing, whereas in the absence of a start codon, aIF2 contributes to swing out the tRNA. This spring force concept highlights a mechanism of codon/anticodon probing by the initiator tRNA directly assisted by aIF2. Initiation factor eIF2, common to eukaryotes and archaea, is a central actor in translation initiation. Here the authors describe two cryo-EM structures of archaeal 30S initiation complexes that provide a novel view of the central role that e/aIF2 plays in start codon selection.
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15
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Abstract
Cells adapt to their environment by linking external stimuli to an intricate network of transcriptional, post-transcriptional and translational processes. Among these, mechanisms that couple environmental cues to the regulation of protein translation are not well understood. Chemical modifications of RNA allow rapid cellular responses to external stimuli by modulating a wide range of fundamental biochemical properties and processes, including the stability, splicing and translation of messenger RNA. In this Review, we focus on the occurrence of N6-methyladenosine (m6A), 5-methylcytosine (m5C) and pseudouridine (Ψ) in RNA, and describe how these RNA modifications are implicated in regulating pluripotency, stem cell self-renewal and fate specification. Both post-transcriptional modifications and the enzymes that catalyse them modulate stem cell differentiation pathways and are essential for normal development.
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Affiliation(s)
- Michaela Frye
- Wellcome Trust - Medical Research Council Cambridge Stem Cell Institute, Department of Genetics, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
| | - Sandra Blanco
- Wellcome Trust - Medical Research Council Cambridge Stem Cell Institute, Department of Genetics, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
- CIC bioGUNE, Bizkaia Technology Park, Building 801A, Derio, Bizkaia 48160, Spain
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16
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Vincent HA, Ziehr B, Moorman NJ. Human Cytomegalovirus Strategies to Maintain and Promote mRNA Translation. Viruses 2016; 8:97. [PMID: 27089357 PMCID: PMC4848592 DOI: 10.3390/v8040097] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Revised: 03/25/2016] [Accepted: 03/31/2016] [Indexed: 02/02/2023] Open
Abstract
mRNA translation requires the ordered assembly of translation initiation factors and ribosomal subunits on a transcript. Host signaling pathways regulate each step in this process to match levels of protein synthesis to environmental cues. In response to infection, cells activate multiple defenses that limit viral protein synthesis, which viruses must counteract to successfully replicate. Human cytomegalovirus (HCMV) inhibits host defenses that limit viral protein expression and manipulates host signaling pathways to promote the expression of both host and viral proteins necessary for virus replication. Here we review key regulatory steps in mRNA translation, and the strategies used by HCMV to maintain protein synthesis in infected cells.
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Affiliation(s)
- Heather A Vincent
- Department of Microbiology & Immunology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
| | - Benjamin Ziehr
- Department of Microbiology & Immunology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
| | - Nathaniel J Moorman
- Department of Microbiology & Immunology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
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17
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Huang HY, Hopper AK. Multiple Layers of Stress-Induced Regulation in tRNA Biology. Life (Basel) 2016; 6:life6020016. [PMID: 27023616 PMCID: PMC4931453 DOI: 10.3390/life6020016] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Revised: 03/14/2016] [Accepted: 03/17/2016] [Indexed: 01/28/2023] Open
Abstract
tRNAs are the fundamental components of the translation machinery as they deliver amino acids to the ribosomes during protein synthesis. Beyond their essential function in translation, tRNAs also function in regulating gene expression, modulating apoptosis and several other biological processes. There are multiple layers of regulatory mechanisms in each step of tRNA biogenesis. For example, tRNA 3′ trailer processing is altered upon nutrient stress; tRNA modification is reprogrammed under various stresses; nuclear accumulation of tRNAs occurs upon nutrient deprivation; tRNA halves accumulate upon oxidative stress. Here we address how environmental stresses can affect nearly every step of tRNA biology and we describe the possible regulatory mechanisms that influence the function or expression of tRNAs under stress conditions.
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Affiliation(s)
- Hsiao-Yun Huang
- Department of Biology, Indiana University, 915 E third St., Myers 300, Bloomington, IN 47405, USA.
| | - Anita K Hopper
- Department of Molecular Genetics and Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA.
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Hu H, Haas SA, Chelly J, Van Esch H, Raynaud M, de Brouwer APM, Weinert S, Froyen G, Frints SGM, Laumonnier F, Zemojtel T, Love MI, Richard H, Emde AK, Bienek M, Jensen C, Hambrock M, Fischer U, Langnick C, Feldkamp M, Wissink-Lindhout W, Lebrun N, Castelnau L, Rucci J, Montjean R, Dorseuil O, Billuart P, Stuhlmann T, Shaw M, Corbett MA, Gardner A, Willis-Owen S, Tan C, Friend KL, Belet S, van Roozendaal KEP, Jimenez-Pocquet M, Moizard MP, Ronce N, Sun R, O'Keeffe S, Chenna R, van Bömmel A, Göke J, Hackett A, Field M, Christie L, Boyle J, Haan E, Nelson J, Turner G, Baynam G, Gillessen-Kaesbach G, Müller U, Steinberger D, Budny B, Badura-Stronka M, Latos-Bieleńska A, Ousager LB, Wieacker P, Rodríguez Criado G, Bondeson ML, Annerén G, Dufke A, Cohen M, Van Maldergem L, Vincent-Delorme C, Echenne B, Simon-Bouy B, Kleefstra T, Willemsen M, Fryns JP, Devriendt K, Ullmann R, Vingron M, Wrogemann K, Wienker TF, Tzschach A, van Bokhoven H, Gecz J, Jentsch TJ, Chen W, Ropers HH, Kalscheuer VM. X-exome sequencing of 405 unresolved families identifies seven novel intellectual disability genes. Mol Psychiatry 2016; 21:133-48. [PMID: 25644381 PMCID: PMC5414091 DOI: 10.1038/mp.2014.193] [Citation(s) in RCA: 208] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Revised: 11/17/2014] [Accepted: 12/08/2014] [Indexed: 12/27/2022]
Abstract
X-linked intellectual disability (XLID) is a clinically and genetically heterogeneous disorder. During the past two decades in excess of 100 X-chromosome ID genes have been identified. Yet, a large number of families mapping to the X-chromosome remained unresolved suggesting that more XLID genes or loci are yet to be identified. Here, we have investigated 405 unresolved families with XLID. We employed massively parallel sequencing of all X-chromosome exons in the index males. The majority of these males were previously tested negative for copy number variations and for mutations in a subset of known XLID genes by Sanger sequencing. In total, 745 X-chromosomal genes were screened. After stringent filtering, a total of 1297 non-recurrent exonic variants remained for prioritization. Co-segregation analysis of potential clinically relevant changes revealed that 80 families (20%) carried pathogenic variants in established XLID genes. In 19 families, we detected likely causative protein truncating and missense variants in 7 novel and validated XLID genes (CLCN4, CNKSR2, FRMPD4, KLHL15, LAS1L, RLIM and USP27X) and potentially deleterious variants in 2 novel candidate XLID genes (CDK16 and TAF1). We show that the CLCN4 and CNKSR2 variants impair protein functions as indicated by electrophysiological studies and altered differentiation of cultured primary neurons from Clcn4(-/-) mice or after mRNA knock-down. The newly identified and candidate XLID proteins belong to pathways and networks with established roles in cognitive function and intellectual disability in particular. We suggest that systematic sequencing of all X-chromosomal genes in a cohort of patients with genetic evidence for X-chromosome locus involvement may resolve up to 58% of Fragile X-negative cases.
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Affiliation(s)
- H Hu
- Department of Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - S A Haas
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - J Chelly
- University Paris Descartes, Paris, France,Centre National de la Recherche Scientifique Unité Mixte de Recherche 8104, Institut National de la Santé et de la Recherche Médicale Unité 1016, Institut Cochin, Paris, France
| | - H Van Esch
- Center for Human Genetics, University Hospitals Leuven, Leuven, Belgium
| | - M Raynaud
- Inserm U930 ‘Imaging and Brain', Tours, France,University François-Rabelais, Tours, France,Centre Hospitalier Régional Universitaire, Service de Génétique, Tours, France
| | - A P M de Brouwer
- Department of Human Genetics, Radboud University Medical Center, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands
| | - S Weinert
- Max-Delbrück-Centrum für Molekulare Medizin, Berlin, Germany,Leibniz-Institut für Molekulare Pharmakologie, Berlin, Germany
| | - G Froyen
- Human Genome Laboratory, VIB Center for the Biology of Disease, Leuven, Belgium,Human Genome Laboratory, Department of Human Genetics, K.U. Leuven, Leuven, Belgium
| | - S G M Frints
- Department of Clinical Genetics, Maastricht University Medical Center, azM, Maastricht, The Netherlands,School for Oncology and Developmental Biology, GROW, Maastricht University, Maastricht, The Netherlands
| | - F Laumonnier
- Inserm U930 ‘Imaging and Brain', Tours, France,University François-Rabelais, Tours, France
| | - T Zemojtel
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - M I Love
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - H Richard
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - A-K Emde
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - M Bienek
- Department of Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - C Jensen
- Department of Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - M Hambrock
- Department of Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - U Fischer
- Department of Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - C Langnick
- Max-Delbrück-Centrum für Molekulare Medizin, Berlin, Germany
| | - M Feldkamp
- Max-Delbrück-Centrum für Molekulare Medizin, Berlin, Germany
| | - W Wissink-Lindhout
- Department of Human Genetics, Radboud University Medical Center, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands
| | - N Lebrun
- University Paris Descartes, Paris, France,Centre National de la Recherche Scientifique Unité Mixte de Recherche 8104, Institut National de la Santé et de la Recherche Médicale Unité 1016, Institut Cochin, Paris, France
| | - L Castelnau
- University Paris Descartes, Paris, France,Centre National de la Recherche Scientifique Unité Mixte de Recherche 8104, Institut National de la Santé et de la Recherche Médicale Unité 1016, Institut Cochin, Paris, France
| | - J Rucci
- University Paris Descartes, Paris, France,Centre National de la Recherche Scientifique Unité Mixte de Recherche 8104, Institut National de la Santé et de la Recherche Médicale Unité 1016, Institut Cochin, Paris, France
| | - R Montjean
- University Paris Descartes, Paris, France,Centre National de la Recherche Scientifique Unité Mixte de Recherche 8104, Institut National de la Santé et de la Recherche Médicale Unité 1016, Institut Cochin, Paris, France
| | - O Dorseuil
- University Paris Descartes, Paris, France,Centre National de la Recherche Scientifique Unité Mixte de Recherche 8104, Institut National de la Santé et de la Recherche Médicale Unité 1016, Institut Cochin, Paris, France
| | - P Billuart
- University Paris Descartes, Paris, France,Centre National de la Recherche Scientifique Unité Mixte de Recherche 8104, Institut National de la Santé et de la Recherche Médicale Unité 1016, Institut Cochin, Paris, France
| | - T Stuhlmann
- Max-Delbrück-Centrum für Molekulare Medizin, Berlin, Germany,Leibniz-Institut für Molekulare Pharmakologie, Berlin, Germany
| | - M Shaw
- School of Paediatrics and Reproductive Health, The University of Adelaide, Adelaide, SA, Australia,Robinson Research Institute, The University of Adelaide, Adelaide, SA, Australia
| | - M A Corbett
- School of Paediatrics and Reproductive Health, The University of Adelaide, Adelaide, SA, Australia,Robinson Research Institute, The University of Adelaide, Adelaide, SA, Australia
| | - A Gardner
- School of Paediatrics and Reproductive Health, The University of Adelaide, Adelaide, SA, Australia,Robinson Research Institute, The University of Adelaide, Adelaide, SA, Australia
| | - S Willis-Owen
- School of Paediatrics and Reproductive Health, The University of Adelaide, Adelaide, SA, Australia,National Heart and Lung Institute, Imperial College London, London, UK
| | - C Tan
- School of Paediatrics and Reproductive Health, The University of Adelaide, Adelaide, SA, Australia
| | - K L Friend
- SA Pathology, Women's and Children's Hospital, Adelaide, SA, Australia
| | - S Belet
- Human Genome Laboratory, VIB Center for the Biology of Disease, Leuven, Belgium,Human Genome Laboratory, Department of Human Genetics, K.U. Leuven, Leuven, Belgium
| | - K E P van Roozendaal
- Department of Clinical Genetics, Maastricht University Medical Center, azM, Maastricht, The Netherlands,School for Oncology and Developmental Biology, GROW, Maastricht University, Maastricht, The Netherlands
| | - M Jimenez-Pocquet
- Centre Hospitalier Régional Universitaire, Service de Génétique, Tours, France
| | - M-P Moizard
- Inserm U930 ‘Imaging and Brain', Tours, France,University François-Rabelais, Tours, France,Centre Hospitalier Régional Universitaire, Service de Génétique, Tours, France
| | - N Ronce
- Inserm U930 ‘Imaging and Brain', Tours, France,University François-Rabelais, Tours, France,Centre Hospitalier Régional Universitaire, Service de Génétique, Tours, France
| | - R Sun
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - S O'Keeffe
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - R Chenna
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - A van Bömmel
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - J Göke
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - A Hackett
- Genetics of Learning and Disability Service, Hunter Genetics, Waratah, NSW, Australia
| | - M Field
- Genetics of Learning and Disability Service, Hunter Genetics, Waratah, NSW, Australia
| | - L Christie
- Genetics of Learning and Disability Service, Hunter Genetics, Waratah, NSW, Australia
| | - J Boyle
- Genetics of Learning and Disability Service, Hunter Genetics, Waratah, NSW, Australia
| | - E Haan
- School of Paediatrics and Reproductive Health, The University of Adelaide, Adelaide, SA, Australia,SA Pathology, Women's and Children's Hospital, Adelaide, SA, Australia
| | - J Nelson
- Genetic Services of Western Australia, King Edward Memorial Hospital, Perth, WA, Australia
| | - G Turner
- Genetics of Learning and Disability Service, Hunter Genetics, Waratah, NSW, Australia
| | - G Baynam
- Genetic Services of Western Australia, King Edward Memorial Hospital, Perth, WA, Australia,School of Paediatrics and Child Health, University of Western Australia, Perth, WA, Australia,Institute for Immunology and Infectious Diseases, Murdoch University, Perth, WA, Australia,Telethon Kids Institute, Perth, WA, Australia
| | | | - U Müller
- Institut für Humangenetik, Justus-Liebig-Universität Giessen, Giessen, Germany,bio.logis Center for Human Genetics, Frankfurt a. M., Germany
| | - D Steinberger
- Institut für Humangenetik, Justus-Liebig-Universität Giessen, Giessen, Germany,bio.logis Center for Human Genetics, Frankfurt a. M., Germany
| | - B Budny
- Chair and Department of Endocrinology, Metabolism and Internal Diseases, Ponzan University of Medical Sciences, Poznan, Poland
| | - M Badura-Stronka
- Chair and Department of Medical Genetics, Poznan University of Medical Sciences, Poznan, Poland
| | - A Latos-Bieleńska
- Chair and Department of Medical Genetics, Poznan University of Medical Sciences, Poznan, Poland
| | - L B Ousager
- Department of Clinical Genetics, Odense University Hospital, Odense, Denmark
| | - P Wieacker
- Institut für Humangenetik, Universitätsklinikum Münster, Muenster, Germany
| | | | - M-L Bondeson
- Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - G Annerén
- Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - A Dufke
- Institut für Medizinische Genetik und Angewandte Genomik, Tübingen, Germany
| | - M Cohen
- Kinderzentrum München, München, Germany
| | - L Van Maldergem
- Centre de Génétique Humaine, Université de Franche-Comté, Besançon, France
| | - C Vincent-Delorme
- Service de Génétique, Hôpital Jeanne de Flandre CHRU de Lilles, Lille, France
| | - B Echenne
- Service de Neuro-Pédiatrie, CHU Montpellier, Montpellier, France
| | - B Simon-Bouy
- Laboratoire SESEP, Centre hospitalier de Versailles, Le Chesnay, France
| | - T Kleefstra
- Department of Human Genetics, Radboud University Medical Center, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands
| | - M Willemsen
- Department of Human Genetics, Radboud University Medical Center, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands
| | - J-P Fryns
- Center for Human Genetics, University Hospitals Leuven, Leuven, Belgium
| | - K Devriendt
- Center for Human Genetics, University Hospitals Leuven, Leuven, Belgium
| | - R Ullmann
- Department of Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - M Vingron
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - K Wrogemann
- Department of Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany,Department of Biochemistry and Medical Genetics, University of Manitoba, Winnipeg, MB, Canada
| | - T F Wienker
- Department of Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - A Tzschach
- Department of Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - H van Bokhoven
- Department of Human Genetics, Radboud University Medical Center, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands
| | - J Gecz
- School of Paediatrics and Reproductive Health, The University of Adelaide, Adelaide, SA, Australia,Robinson Research Institute, The University of Adelaide, Adelaide, SA, Australia
| | - T J Jentsch
- Max-Delbrück-Centrum für Molekulare Medizin, Berlin, Germany,Leibniz-Institut für Molekulare Pharmakologie, Berlin, Germany
| | - W Chen
- Department of Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany,Max-Delbrück-Centrum für Molekulare Medizin, Berlin, Germany
| | - H-H Ropers
- Department of Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - V M Kalscheuer
- Department of Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany,Max Planck Institute for Molecular Genetics, Ihnestrasse 73, Berlin 14195, Germany. E-mail:
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19
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Perez WB, Kinzy TG. Translation elongation factor 1A mutants with altered actin bundling activity show reduced aminoacyl-tRNA binding and alter initiation via eIF2α phosphorylation. J Biol Chem 2015; 289:20928-38. [PMID: 24936063 DOI: 10.1074/jbc.m114.570077] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Apart from its canonical function in translation elongation, eukaryotic translation elongation factor 1A (eEF1A) has been shown to interact with the actin cytoskeleton. Amino acid substitutions in eEF1A that reduce its ability to bind and bundle actin in vitro cause improper actin organization in vivo and reduce total translation. Initial in vivo analysis indicated the reduced translation was through initiation. The mutant strains exhibit increased levels of phosphorylated initiation factor 2α (eIF2α) dependent on the presence of the general control non-derepressible 2 (Gcn2p) protein kinase. Gcn2p causes downregulation of total protein synthesis at initiation in response to increases in deacylated tRNA levels in the cell. Increased levels of eIF2α phosphorylation are not due to a general reduction in translation elongation as eEF2 and eEF3 mutants do not exhibit this effect. Deletion of GCN2 from the eEF1A actin bundling mutant strains revealed a second defect in translation. The eEF1A actin-bundling proteins exhibit changes in their elongation activity at the level of aminoacyl-tRNA binding in vitro. These findings implicate eEF1A in a feedback mechanism for regulating translation at initiation.
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20
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Zhang F, Saini AK, Shin BS, Nanda J, Hinnebusch AG. Conformational changes in the P site and mRNA entry channel evoked by AUG recognition in yeast translation preinitiation complexes. Nucleic Acids Res 2015; 43:2293-312. [PMID: 25670678 PMCID: PMC4344491 DOI: 10.1093/nar/gkv028] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The translation preinitiation complex (PIC) is thought to assume an open conformation when scanning the mRNA leader, with AUG recognition evoking a closed conformation and more stable P site interaction of Met-tRNAi; however, physical evidence is lacking that AUG recognition constrains interaction of mRNA with the 40S binding cleft. We compared patterns of hydroxyl radical cleavage of rRNA by Fe(II)-BABE tethered to unique sites in eIF1A in yeast PICs reconstituted with mRNA harboring an AUG or near-cognate (AUC) start codon. rRNA residues in the P site display reduced cleavage in AUG versus AUC PICs; and enhanced cleavage in the AUC complexes was diminished by mutations of scanning enhancer elements of eIF1A that increase near-cognate recognition in vivo. This suggests that accessibility of these rRNA residues is reduced by accommodation of Met-tRNAi in the P site (PIN state) and by their interactions with the anticodon stem of Met-tRNAi. Our cleavage data also provide evidence that AUG recognition evokes dissociation of eIF1 from its 40S binding site, ejection of the eIF1A-CTT from the P-site and rearrangement to a closed conformation of the entry channel with reduced mobility of mRNA.
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Affiliation(s)
- Fan Zhang
- Laboratory of Gene Regulation and Development, NICHD, NIH, Bethesda, MD 20892, USA
| | - Adesh K Saini
- Laboratory of Gene Regulation and Development, NICHD, NIH, Bethesda, MD 20892, USA Department of Biotechnology, Shoolini University of Biotechnology and Management Sciences, Solan, Himachal Pradesh-173212, India
| | - Byung-Sik Shin
- Laboratory of Gene Regulation and Development, NICHD, NIH, Bethesda, MD 20892, USA
| | - Jagpreet Nanda
- Laboratory on the Mechanism and Regulation of Protein Synthesis, NICHD, NIH, Bethesda, MD 20892, USA
| | - Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, NICHD, NIH, Bethesda, MD 20892, USA
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21
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Ghosh A, Komar AA. Eukaryote-specific extensions in ribosomal proteins of the small subunit: Structure and function. ACTA ACUST UNITED AC 2015; 3:e999576. [PMID: 26779416 DOI: 10.1080/21690731.2014.999576] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Revised: 12/03/2014] [Accepted: 12/12/2014] [Indexed: 01/05/2023]
Abstract
High-resolution structures of yeast ribosomes have improved our understanding of the architecture and organization of eukaryotic rRNA and proteins, as well as eukaryote-specific extensions present in some conserved ribosomal proteins. Despite this progress, assignment of specific functions to individual proteins and/or eukaryote-specific protein extensions remains challenging. It has been suggested that eukaryote-specific extensions of conserved proteins from the small ribosomal subunit may facilitate eukaryote-specific reactions in the initiation phase of protein synthesis. This review summarizes emerging data describing the structural and functional significance of eukaryote-specific extensions of conserved small ribosomal subunit proteins, particularly their possible roles in recruitment and spatial organization of eukaryote-specific initiation factors.
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Affiliation(s)
- Arnab Ghosh
- Center for Gene Regulation in Health and Disease; Department of Biological, Geological and Environmental Sciences; Cleveland State University ; Cleveland, OH USA
| | - Anton A Komar
- Center for Gene Regulation in Health and Disease; Department of Biological, Geological and Environmental Sciences; Cleveland State University ; Cleveland, OH USA
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22
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Abstract
Cellular RNAs can be chemically modified over a hundred different ways. These modifications were once thought to be static, discrete, and utilized to fine-tune RNA structure and function. However, recent studies have revealed that some modifications, like mRNA methylation, can be reversed, and these reversible modifications may play active roles in regulating diverse biological processes. In this perspective, we summarize examples of dynamic RNA modifications that affect biological functions. We further propose that reversible modifications might occur on tRNA, rRNA, and other noncoding RNAs to regulate gene expression analogous to the reversible mRNA methylation.
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23
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Hussain T, Llácer JL, Fernández IS, Munoz A, Martin-Marcos P, Savva CG, Lorsch JR, Hinnebusch AG, Ramakrishnan V. Structural changes enable start codon recognition by the eukaryotic translation initiation complex. Cell 2014; 159:597-607. [PMID: 25417110 PMCID: PMC4217140 DOI: 10.1016/j.cell.2014.10.001] [Citation(s) in RCA: 143] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 08/15/2014] [Accepted: 10/01/2014] [Indexed: 11/03/2022]
Abstract
During eukaryotic translation initiation, initiator tRNA does not insert fully into the P decoding site on the 40S ribosomal subunit. This conformation (POUT) is compatible with scanning mRNA for the AUG start codon. Base pairing with AUG is thought to promote isomerization to a more stable conformation (PIN) that arrests scanning and promotes dissociation of eIF1 from the 40S subunit. Here, we present a cryoEM reconstruction of a yeast preinitiation complex at 4.0 Å resolution with initiator tRNA in the PIN state, prior to eIF1 release. The structure reveals stabilization of the codon-anticodon duplex by the N-terminal tail of eIF1A, changes in the structure of eIF1 likely instrumental in its subsequent release, and changes in the conformation of eIF2. The mRNA traverses the entire mRNA cleft and makes connections to the regulatory domain of eIF2?, eIF1A, and ribosomal elements that allow recognition of context nucleotides surrounding the AUG codon.
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Affiliation(s)
| | - Jose L Llácer
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK
| | | | - Antonio Munoz
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Pilar Martin-Marcos
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | | | - Jon R Lorsch
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - V Ramakrishnan
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
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24
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Upregulation of eIF5B controls cell-cycle arrest and specific developmental stages. Proc Natl Acad Sci U S A 2014; 111:E4315-22. [PMID: 25261552 DOI: 10.1073/pnas.1320477111] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Proliferation arrest and distinct developmental stages alter and decrease general translation yet maintain ongoing translation. The factors that support translation in these conditions remain to be characterized. We investigated an altered translation factor in three cell states considered to have reduced general translation: immature Xenopus laevis oocytes, mouse ES cells, and the transition state of proliferating mammalian cells to quiescence (G0) upon growth-factor deprivation. Our data reveal a transient increase of eukaryotic translation initiation factor 5B (eIF5B), the eukaryotic ortholog of bacterial initiation factor IF2, in these conditions. eIF5B promotes 60S ribosome subunit joining and pre-40S subunit proofreading. eIF5B has also been shown to promote the translation of viral and stress-related mRNAs and can contribute indirectly to supporting or stabilizing initiator methionyl tRNA (tRNA-Met(i)) association with the ribosome. We find that eIF5B is a limiting factor for translation in these three conditions. The increased eIF5B levels lead to increased eIF5B complexes with tRNA-Met(i) upon serum starvation of THP1 mammalian cells. In addition, increased phosphorylation of eukaryotic initiation factor 2α, the translation factor that recruits initiator tRNA-Meti for general translation, is observed in these conditions. Importantly, we find that eIF5B is an antagonist of G0 and G0-like states, as eIF5B depletion reduces maturation of G0-like, immature oocytes and hastens early G0 arrest in serum-starved THP1 cells. Consistently, eIF5B overexpression promotes maturation of G0-like immature oocytes and causes cell death, an alternative to G0, in serum-starved THP1 cells. These data reveal a critical role for a translation factor that regulates specific cell-cycle transition and developmental stages.
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25
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Sokabe M, Fraser CS. Human eukaryotic initiation factor 2 (eIF2)-GTP-Met-tRNAi ternary complex and eIF3 stabilize the 43 S preinitiation complex. J Biol Chem 2014; 289:31827-31836. [PMID: 25246524 DOI: 10.1074/jbc.m114.602870] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The formation of a stable 43 S preinitiation complex (PIC) must occur to enable successful mRNA recruitment. However, the contributions of eIF1, eIF1A, eIF3, and the eIF2-GTP-Met-tRNAi ternary complex (TC) in stabilizing the 43 S PIC are poorly defined. We have reconstituted the human 43 S PIC and used fluorescence anisotropy to systematically measure the affinity of eIF1, eIF1A, and eIF3j in the presence of different combinations of 43 S PIC components. Our data reveal a complicated network of interactions that result in high affinity binding of all 43 S PIC components with the 40 S subunit. Human eIF1 and eIF1A bind cooperatively to the 40 S subunit, revealing an evolutionarily conserved interaction. Negative cooperativity is observed between the binding of eIF3j and the binding of eIF1, eIF1A, and TC with the 40 S subunit. To overcome this, eIF3 dramatically increases the affinity of eIF1 and eIF3j for the 40 S subunit. Recruitment of TC also increases the affinity of eIF1 for the 40 S subunit, but this interaction has an important indirect role in increasing the affinity of eIF1A for the 40 S subunit. Together, our data provide a more complete thermodynamic framework of the human 43 S PIC and reveal important interactions between its components to maintain its stability.
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Affiliation(s)
- Masaaki Sokabe
- Department of Molecular and Cellular Biology, College of Biological Sciences, University of California, Davis, California 95616
| | - Christopher S Fraser
- Department of Molecular and Cellular Biology, College of Biological Sciences, University of California, Davis, California 95616.
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26
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Conserved residues in yeast initiator tRNA calibrate initiation accuracy by regulating preinitiation complex stability at the start codon. Genes Dev 2014; 28:502-20. [PMID: 24589778 PMCID: PMC3950347 DOI: 10.1101/gad.236547.113] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Eukaryotic initiator tRNA (tRNAi) contains several highly conserved, unique sequence features, yet their importance in accurate start codon selection is unknown. Using genetic and biochemical analyses, Dong et al. show that conserved bases throughout tRNAi, from the anticodon stem to the acceptor stem, play key roles in ensuring the fidelity of start codon recognition. This work delineates specific molecular functions for signature initiator tRNA residues and establishes their importance for initiation accuracy in living eukaryotic cells. Eukaryotic initiator tRNA (tRNAi) contains several highly conserved unique sequence features, but their importance in accurate start codon selection was unknown. Here we show that conserved bases throughout tRNAi, from the anticodon stem to acceptor stem, play key roles in ensuring the fidelity of start codon recognition in yeast cells. Substituting the conserved G31:C39 base pair in the anticodon stem with different pairs reduces accuracy (the Sui− [suppressor of initiation codon] phenotype), whereas eliminating base pairing increases accuracy (the Ssu− [suppressor of Sui−] phenotype). The latter defect is fully suppressed by a Sui− substitution of T-loop residue A54. These genetic data are paralleled by opposing effects of Sui− and Ssu− substitutions on the stability of methionylated tRNAi (Met-tRNAi) binding (in the ternary complex [TC] with eIF2-GTP) to reconstituted preinitiation complexes (PICs). Disrupting the C3:G70 base pair in the acceptor stem produces a Sui− phenotype and also reduces the rate of TC binding to 40S subunits in vitro and in vivo. Both defects are suppressed by an Ssu− substitution in eIF1A that stabilizes the open/POUT conformation of the PIC that exists prior to start codon recognition. Our data indicate that these signature sequences of tRNAi regulate accuracy by distinct mechanisms, promoting the open/POUT conformation of the PIC (for C3:G70) or destabilizing the closed/PIN state (for G31:C39 and A54) that is critical for start codon recognition.
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Protein phosphatase PP1/GLC7 interaction domain in yeast eIF2γ bypasses targeting subunit requirement for eIF2α dephosphorylation. Proc Natl Acad Sci U S A 2014; 111:E1344-53. [PMID: 24706853 DOI: 10.1073/pnas.1400129111] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Whereas the protein kinases GCN2, HRI, PKR, and PERK specifically phosphorylate eukaryotic translation initiation factor 2 (eIF2α) on Ser51 to regulate global and gene-specific mRNA translation, eIF2α is dephosphorylated by the broadly acting serine/threonine protein phosphatase 1 (PP1). In mammalian cells, the regulatory subunits GADD34 and CReP target PP1 to dephosphorylate eIF2α; however, as there are no homologs of these targeting subunits in yeast, it is unclear how GLC7, the functional homolog of PP1 in yeast, is recruited to dephosphorylate eIF2α. Here, we show that a novel N-terminal extension on yeast eIF2γ contains a PP1-binding motif (KKVAF) that enables eIF2γ to pull down GLC7 and target it to dephosphorylate eIF2α. Truncation or point mutations designed to eliminate the KKVAF motif in eIF2γ impair eIF2α dephosphorylation in vivo and in vitro and enhance expression of GCN4. Replacement of the N terminus of eIF2γ with the GLC7-binding domain from GAC1 or fusion of heterologous dimerization domains to eIF2γ and GLC7, respectively, maintained eIF2α phosphorylation at basal levels. Taken together, these results indicate that, in contrast to the paradigm of distinct PP1-targeting or regulatory subunits, the unique N terminus of yeast eIF2γ functions in cis to target GLC7 to dephosphorylate eIF2α.
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Abstract
In eukaryotes, the translation initiation codon is generally identified by the scanning mechanism, wherein every triplet in the messenger RNA leader is inspected for complementarity to the anticodon of methionyl initiator transfer RNA (Met-tRNAi). Binding of Met-tRNAi to the small (40S) ribosomal subunit, in a ternary complex (TC) with eIF2-GTP, is stimulated by eukaryotic initiation factor 1 (eIF1), eIF1A, eIF3, and eIF5, and the resulting preinitiation complex (PIC) joins the 5' end of mRNA preactivated by eIF4F and poly(A)-binding protein. RNA helicases remove secondary structures that impede ribosome attachment and subsequent scanning. Hydrolysis of eIF2-bound GTP is stimulated by eIF5 in the scanning PIC, but completion of the reaction is impeded at non-AUG triplets. Although eIF1 and eIF1A promote scanning, eIF1 and possibly the C-terminal tail of eIF1A must be displaced from the P decoding site to permit base-pairing between Met-tRNAi and the AUG codon, as well as to allow subsequent phosphate release from eIF2-GDP. A second GTPase, eIF5B, catalyzes the joining of the 60S subunit to produce an 80S initiation complex that is competent for elongation.
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Affiliation(s)
- Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892;
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29
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Transfer RNA post-transcriptional processing, turnover, and subcellular dynamics in the yeast Saccharomyces cerevisiae. Genetics 2013; 194:43-67. [PMID: 23633143 DOI: 10.1534/genetics.112.147470] [Citation(s) in RCA: 145] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Transfer RNAs (tRNAs) are essential for protein synthesis. In eukaryotes, tRNA biosynthesis employs a specialized RNA polymerase that generates initial transcripts that must be subsequently altered via a multitude of post-transcriptional steps before the tRNAs beome mature molecules that function in protein synthesis. Genetic, genomic, biochemical, and cell biological approaches possible in the powerful Saccharomyces cerevisiae system have led to exciting advances in our understandings of tRNA post-transcriptional processing as well as to novel insights into tRNA turnover and tRNA subcellular dynamics. tRNA processing steps include removal of transcribed leader and trailer sequences, addition of CCA to the 3' mature sequence and, for tRNA(His), addition of a 5' G. About 20% of yeast tRNAs are encoded by intron-containing genes. The three-step splicing process to remove the introns surprisingly occurs in the cytoplasm in yeast and each of the splicing enzymes appears to moonlight in functions in addition to tRNA splicing. There are 25 different nucleoside modifications that are added post-transcriptionally, creating tRNAs in which ∼15% of the residues are nucleosides other than A, G, U, or C. These modified nucleosides serve numerous important functions including tRNA discrimination, translation fidelity, and tRNA quality control. Mature tRNAs are very stable, but nevertheless yeast cells possess multiple pathways to degrade inappropriately processed or folded tRNAs. Mature tRNAs are also dynamic in cells, moving from the cytoplasm to the nucleus and back again to the cytoplasm; the mechanism and function of this retrograde process is poorly understood. Here, the state of knowledge for tRNA post-transcriptional processing, turnover, and subcellular dynamics is addressed, highlighting the questions that remain.
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Sharifulin D, Babaylova E, Kossinova O, Bartuli Y, Graifer D, Karpova G. Ribosomal protein S5e is implicated in translation initiation through its interaction with the N-terminal domain of initiation factor eIF2α. Chembiochem 2013; 14:2136-43. [PMID: 24106102 DOI: 10.1002/cbic.201300318] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Indexed: 12/30/2022]
Abstract
A key step of translation initiation in eukaryotes is formation of the 48S preinitiation complex (PIC) containing the 40S ribosome, a set of eukaryotic initiation factors (eIFs), mRNA, and initiator Met-tRNA interacting with mRNA start codon; however, the PIC structure remains substantially unknown. Here, we apply formaldehyde-induced protein-protein crosslinks to identify contacts between ribosomal protein S5e (rpS5e, "e" stands for "eukaryotic") and eIFs within the mammalian PIC, assembled on either model canonical or IRES-containing mRNA. Using immunoblotting and mass spectrometry, we show that with both types of mRNA, rpS5e crosslinks to eIF2α. Comparative analysis of peptides resulting from trypsinolysis of the crosslinked proteins before and after crosslink reversal reveals crosslinked peptides in the N-terminal parts of rpS5e and eIF2α. Application of these data to a model PIC structure obtained with the use of available structures indicates that eIF2α undergoes major conformation rearrangements to enable contacts of the factor with rpS5e. These contacts are suggested to maintain the correct positioning of eIF2α relative to other PIC components; this could be essential for start-codon selection by the PIC.
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Affiliation(s)
- Dmitri Sharifulin
- Laboratory of Ribosome Structure and Functions, Institute of Chemical Biology and Fundamental Medicine, Siberian Branch of the Russian Academy of Sciences, Prospekt Lavrentieva 8, Novosibirsk, 630090 (Russia); Department of Molecular Biology, Novosibirsk State University, Ulitsa Pirogova 2, Novosibirsk, 630090 (Russia)
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Hashem Y, des Georges A, Dhote V, Langlois R, Liao HY, Grassucci RA, Hellen CUT, Pestova TV, Frank J. Structure of the mammalian ribosomal 43S preinitiation complex bound to the scanning factor DHX29. Cell 2013; 153:1108-19. [PMID: 23706745 DOI: 10.1016/j.cell.2013.04.036] [Citation(s) in RCA: 158] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 03/06/2013] [Accepted: 04/05/2013] [Indexed: 01/19/2023]
Abstract
Eukaryotic translation initiation begins with assembly of a 43S preinitiation complex. First, methionylated initiator methionine transfer RNA (Met-tRNAi(Met)), eukaryotic initiation factor (eIF) 2, and guanosine triphosphate form a ternary complex (TC). The TC, eIF3, eIF1, and eIF1A cooperatively bind to the 40S subunit, yielding the 43S preinitiation complex, which is ready to attach to messenger RNA (mRNA) and start scanning to the initiation codon. Scanning on structured mRNAs additionally requires DHX29, a DExH-box protein that also binds directly to the 40S subunit. Here, we present a cryo-electron microscopy structure of the mammalian DHX29-bound 43S complex at 11.6 Å resolution. It reveals that eIF2 interacts with the 40S subunit via its α subunit and supports Met-tRNAi(Met) in an unexpected P/I orientation (eP/I). The structural core of eIF3 resides on the back of the 40S subunit, establishing two principal points of contact, whereas DHX29 binds around helix 16. The structure provides insights into eukaryote-specific aspects of translation, including the mechanism of action of DHX29.
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Affiliation(s)
- Yaser Hashem
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
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32
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Weisser M, Voigts-Hoffmann F, Rabl J, Leibundgut M, Ban N. The crystal structure of the eukaryotic 40S ribosomal subunit in complex with eIF1 and eIF1A. Nat Struct Mol Biol 2013; 20:1015-7. [PMID: 23851459 DOI: 10.1038/nsmb.2622] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Accepted: 05/23/2013] [Indexed: 11/09/2022]
Abstract
Eukaryotic translation initiation factors (eIFs) 1A and 1 are central players in the complex process of start-codon recognition. To improve mechanistic understanding of this process, we determined the crystal structure of the 40S ribosomal subunit in complex with eIF1A and eIF1 from Tetrahymena thermophila at a resolution of 3.7 Å. It reveals the positions of the two factors on the 40S and the conformational changes that accompany their binding.
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Affiliation(s)
- Melanie Weisser
- Institute of Molecular Biology and Biophysics, Swiss Federal Institute of Technology (ETH Zürich), Zürich, Switzerland
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Gutierrez E, Shin BS, Woolstenhulme CJ, Kim JR, Saini P, Buskirk AR, Dever TE. eIF5A promotes translation of polyproline motifs. Mol Cell 2013; 51:35-45. [PMID: 23727016 PMCID: PMC3744875 DOI: 10.1016/j.molcel.2013.04.021] [Citation(s) in RCA: 338] [Impact Index Per Article: 30.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Revised: 04/10/2013] [Accepted: 04/25/2013] [Indexed: 11/17/2022]
Abstract
Translation factor eIF5A, containing the unique amino acid hypusine, was originally shown to stimulate Met-puromycin synthesis, a model assay for peptide bond formation. More recently, eIF5A was shown to promote translation elongation; however, its precise requirement in protein synthesis remains elusive. We use in vivo assays in yeast and in vitro reconstituted translation assays to reveal a specific requirement for eIF5A to promote peptide bond formation between consecutive Pro residues. Addition of eIF5A relieves ribosomal stalling during translation of three consecutive Pro residues in vitro, and loss of eIF5A function impairs translation of polyproline-containing proteins in vivo. Hydroxyl radical probing experiments localized eIF5A near the E site of the ribosome with its hypusine residue adjacent to the acceptor stem of the P site tRNA. Thus, eIF5A, like its bacterial ortholog EFP, is proposed to stimulate the peptidyl transferase activity of the ribosome and facilitate the reactivity of poor substrates like Pro.
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Affiliation(s)
- Erik Gutierrez
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
- Department of Biology, Johns Hopkins University, Baltimore, MD, USA
| | - Byung-Sik Shin
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | | | - Joo-Ran Kim
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Preeti Saini
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Allen R. Buskirk
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT, USA
| | - Thomas E. Dever
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
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Interaction between 25S rRNA A loop and eukaryotic translation initiation factor 5B promotes subunit joining and ensures stringent AUG selection. Mol Cell Biol 2013; 33:3540-8. [PMID: 23836883 DOI: 10.1128/mcb.00771-13] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
In yeast, 25S rRNA makes up the major mass and shape of the 60S ribosomal subunit. During the last step of translation initiation, eukaryotic initiation factor 5B (eIF5B) promotes the 60S subunit joining with the 40S initiation complex (IC). Malfunctional 60S subunits produced by misfolding or mutation may disrupt the 40S IC stalling on the start codon, thereby altering the stringency of initiation. Using several point mutations isolated by random mutagenesis, here we studied the role of 25S rRNA in start codon selection. Three mutations changing bases near the ribosome surface had strong effects, allowing the initiating ribosomes to skip both AUG and non-AUG codons: C2879U and U2408C, altering the A loop and P loop, respectively, of the peptidyl transferase center, and G1735A, mapping near a Eukarya-specific bridge to the 40S subunit. Overexpression of eIF5B specifically suppressed the phenotype caused by C2879U, suggesting functional interaction between eIF5B and the A loop. In vitro reconstitution assays showed that C2879U decreased eIF5B-catalyzed 60S subunit joining with a 40S IC. Thus, eIF5B interaction with the peptidyl transferase center A loop increases the accuracy of initiation by stabilizing the overall conformation of the 80S initiation complex. This study provides an insight into the effect of ribosomal mutations on translation profiles in eukaryotes.
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Valásek LS. 'Ribozoomin'--translation initiation from the perspective of the ribosome-bound eukaryotic initiation factors (eIFs). Curr Protein Pept Sci 2013; 13:305-30. [PMID: 22708493 PMCID: PMC3434475 DOI: 10.2174/138920312801619385] [Citation(s) in RCA: 103] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2011] [Revised: 01/16/2012] [Accepted: 02/16/2012] [Indexed: 02/05/2023]
Abstract
Protein synthesis is a fundamental biological mechanism bringing the DNA-encoded genetic information into
life by its translation into molecular effectors - proteins. The initiation phase of translation is one of the key points of gene
regulation in eukaryotes, playing a role in processes from neuronal function to development. Indeed, the importance of the
study of protein synthesis is increasing with the growing list of genetic diseases caused by mutations that affect mRNA
translation. To grasp how this regulation is achieved or altered in the latter case, we must first understand the molecular
details of all underlying processes of the translational cycle with the main focus put on its initiation. In this review I discuss
recent advances in our comprehension of the molecular basis of particular initiation reactions set into the context of
how and where individual eIFs bind to the small ribosomal subunit in the pre-initiation complex. I also summarize our
current knowledge on how eukaryotic initiation factor eIF3 controls gene expression in the gene-specific manner via reinitiation.
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Affiliation(s)
- Leos Shivaya Valásek
- Laboratory of Eukaryotic Gene Regulation, Institute of Microbiology AS CR, Prague, Czech Republic.
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36
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Walker SE, Zhou F, Mitchell SF, Larson VS, Valasek L, Hinnebusch AG, Lorsch JR. Yeast eIF4B binds to the head of the 40S ribosomal subunit and promotes mRNA recruitment through its N-terminal and internal repeat domains. RNA (NEW YORK, N.Y.) 2013; 19:191-207. [PMID: 23236192 PMCID: PMC3543093 DOI: 10.1261/rna.035881.112] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Accepted: 11/13/2012] [Indexed: 05/20/2023]
Abstract
Eukaryotic translation initiation factor (eIF)4B stimulates recruitment of mRNA to the 43S ribosomal pre-initiation complex (PIC). Yeast eIF4B (yeIF4B), shown previously to bind single-stranded (ss) RNA, consists of an N-terminal domain (NTD), predicted to be unstructured in solution; an RNA-recognition motif (RRM); an unusual domain comprised of seven imperfect repeats of 26 amino acids; and a C-terminal domain. Although the mechanism of yeIF4B action has remained obscure, most models have suggested central roles for its RRM and ssRNA-binding activity. We have dissected the functions of yeIF4B's domains and show that the RRM and its ssRNA-binding activity are dispensable in vitro and in vivo. Instead, our data indicate that the 7-repeats and NTD are the most critical domains, which mediate binding of yeIF4B to the head of the 40S ribosomal subunit via interaction with Rps20. This interaction induces structural changes in the ribosome's mRNA entry channel that could facilitate mRNA loading. We also show that yeIF4B strongly promotes productive interaction of eIF4A with the 43S•mRNA PIC in a manner required for efficient mRNA recruitment.
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MESH Headings
- Amino Acid Sequence
- Amino Acid Substitution
- Eukaryotic Initiation Factor-4A/genetics
- Eukaryotic Initiation Factor-4A/metabolism
- Eukaryotic Initiation Factors/genetics
- Eukaryotic Initiation Factors/metabolism
- Models, Molecular
- Molecular Sequence Data
- Peptide Chain Initiation, Translational
- Polyribosomes/chemistry
- Polyribosomes/metabolism
- Protein Binding
- Protein Biosynthesis
- Protein Structure, Tertiary
- RNA, Fungal/genetics
- RNA, Fungal/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Ribosomal, 18S/chemistry
- RNA, Ribosomal, 18S/metabolism
- RNA-Binding Proteins/genetics
- RNA-Binding Proteins/metabolism
- Ribosomal Proteins/metabolism
- Ribosome Subunits, Small, Eukaryotic/chemistry
- Ribosome Subunits, Small, Eukaryotic/metabolism
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae/growth & development
- Saccharomyces cerevisiae/metabolism
- Saccharomyces cerevisiae Proteins/genetics
- Saccharomyces cerevisiae Proteins/metabolism
- Sequence Alignment
- Sequence Deletion
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Affiliation(s)
- Sarah E. Walker
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | - Fujun Zhou
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Sarah F. Mitchell
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | - Victoria S. Larson
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | - Leos Valasek
- Laboratory of Regulation of Gene Expression, Institute of Microbiology ASCR, v.v.i., Prague 142 20, the Czech Republic
| | - Alan G. Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
- Corresponding authorsE-mailE-mail
| | - Jon R. Lorsch
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
- Corresponding authorsE-mailE-mail
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A yeast purification system for human translation initiation factors eIF2 and eIF2Bε and their use in the diagnosis of CACH/VWM disease. PLoS One 2013; 8:e53958. [PMID: 23335982 PMCID: PMC3545922 DOI: 10.1371/journal.pone.0053958] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Accepted: 12/04/2012] [Indexed: 11/19/2022] Open
Abstract
Recessive inherited mutations in any of five subunits of the general protein synthesis factor eIF2B are responsible for a white mater neurodegenerative disease with a large clinical spectrum. The classical form is called Childhood Ataxia with CNS hypomyelination (CACH) or Vanishing White Matter Leukoencephalopathy (VWM). eIF2B-related disorders affect glial cells, despite the fact that eIF2B is a ubiquitous protein that functions as a guanine-nucleotide exchange factor (GEF) for its partner protein eIF2 in the translation initiation process in all eukaryotic cells. Decreased eIF2B activity measured by a GEF assay in patients' immortalised lymphocytic cells provides a biochemical diagnostic assay but is limited by the availability of eIF2 protein, which is classically purified from a mammalian cell source by column chromatography. Here we describe the generation of a recombinant expression system to produce purified human eIF2 from yeast cells. We demonstrate that human eIF2 can function in yeast cells in place of the equivalent yeast factor. We purify human eIF2 and the C-terminal domain of human eIF2Bε using affinity chromatography from engineered yeast cells and find that both function in a GEF assay: the first demonstration that this human eIF2Bε domain has GEF function. We show that CACH/VWM mutations within this domain reduce its activity. Finally we demonstrate that the recombinant eIF2 functions similarly to eIF2 purified from rat liver in GEF assays with CACH/VWM eIF2B-mutated patient derived lymphocytic cells.
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Stolboushkina E, Nikonov S, Zelinskaya N, Arkhipova V, Nikulin A, Garber M, Nikonov O. Crystal structure of the archaeal translation initiation factor 2 in complex with a GTP analogue and Met-tRNAf(Met.). J Mol Biol 2013; 425:989-98. [PMID: 23291527 DOI: 10.1016/j.jmb.2012.12.023] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2012] [Revised: 10/24/2012] [Accepted: 12/26/2012] [Indexed: 11/29/2022]
Abstract
Heterotrimeric aIF2αβγ (archaeal homologue of the eukaryotic translation initiation factor 2) in its GTP-bound form delivers Met-tRNAi(Met) to the small ribosomal subunit. It is known that the heterodimer containing the GTP-bound γ subunit and domain 3 of the α subunit of aIF2 is required for the formation of a stable complex with Met-tRNAi. Here, the crystal structure of an incomplete ternary complex including aIF2αD3γ⋅GDPNP⋅Met-tRNAf(Met) has been solved at 3.2Å resolution. This structure is in good agreement with biochemical and hydroxyl radical probing data. The analysis of the complex shows that despite the structural similarity of aIF2γ and the bacterial translation elongation factor EF-Tu, their modes of tRNA binding are very different. Remarkably, the recently published 5.0-Å-resolution structure of almost the same ternary initiation complex differs dramatically from the structure presented. Reasons for this discrepancy are discussed.
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Affiliation(s)
- Elena Stolboushkina
- Institute of Protein Research, Russian Academy of Sciences, 142290, Pushchino, Moscow Region, Russian Federation
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Naveau M, Lazennec-Schurdevin C, Panvert M, Dubiez E, Mechulam Y, Schmitt E. Roles of yeast eIF2α and eIF2β subunits in the binding of the initiator methionyl-tRNA. Nucleic Acids Res 2013; 41:1047-57. [PMID: 23193270 PMCID: PMC3553985 DOI: 10.1093/nar/gks1180] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2012] [Revised: 10/19/2012] [Accepted: 10/26/2012] [Indexed: 01/09/2023] Open
Abstract
Heterotrimeric eukaryotic/archaeal translation initiation factor 2 (e/aIF2) binds initiator methionyl-tRNA and plays a key role in the selection of the start codon on messenger RNA. tRNA binding was extensively studied in the archaeal system. The γ subunit is able to bind tRNA, but the α subunit is required to reach high affinity whereas the β subunit has only a minor role. In Saccharomyces cerevisiae however, the available data suggest an opposite scenario with β having the most important contribution to tRNA-binding affinity. In order to overcome difficulties with purification of the yeast eIF2γ subunit, we designed chimeric eIF2 by assembling yeast α and β subunits to archaeal γ subunit. We show that the β subunit of yeast has indeed an important role, with the eukaryote-specific N- and C-terminal domains being necessary to obtain full tRNA-binding affinity. The α subunit apparently has a modest contribution. However, the positive effect of α on tRNA binding can be progressively increased upon shortening the acidic C-terminal extension. These results, together with small angle X-ray scattering experiments, support the idea that in yeast eIF2, the tRNA molecule is bound by the α subunit in a manner similar to that observed in the archaeal aIF2-GDPNP-tRNA complex.
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Affiliation(s)
| | | | | | | | | | - Emmanuelle Schmitt
- Laboratoire de Biochimie, Unité mixte de Recherche 7654, Ecole Polytechnique, Centre National de la Recherche Scientifique, F-91128 Palaiseau Cedex, France
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40
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Protein-protein interactions and multi-component complexes of aminoacyl-tRNA synthetases. Top Curr Chem (Cham) 2013; 344:119-44. [PMID: 24072587 DOI: 10.1007/128_2013_479] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Protein-protein interaction occurs transiently or stably when two or more proteins bind together to mediate a wide range of cellular processes such as protein modification, signal transduction, protein trafficking, and structural folding. The macromolecules involved in protein biosynthesis such as aminoacyl-tRNA synthetase (ARS) have a number of protein-protein interactions. The mammalian multi-tRNA synthetase complex (MSC) consists of eight different enzymes: EPRS, IRS, LRS, QRS, MRS, KRS, RRS, and DRS, and three auxiliary proteins: AIMP1/p43, AIMP2/p38, and AIMP/p18. The distinct ARS proteins are also connected to diverse protein networks to carry out biological functions. In this chapter we first show the protein networks of the entire MSC and explain how MSC components interact with or can regulate other proteins. Finally, it is pointed out that the understanding of protein-protein interaction mechanism will provide insight to potential therapeutic application for diseases related to the MSC network.
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41
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Voigts-Hoffmann F, Klinge S, Ban N. Structural insights into eukaryotic ribosomes and the initiation of translation. Curr Opin Struct Biol 2012; 22:768-77. [DOI: 10.1016/j.sbi.2012.07.010] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Revised: 07/09/2012] [Accepted: 07/10/2012] [Indexed: 01/05/2023]
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Chien KY, Blackburn K, Liu HC, Goshe MB. Proteomic and phosphoproteomic analysis of chicken embryo fibroblasts infected with cell culture-attenuated and vaccine strains of Marek's disease virus. J Proteome Res 2012; 11:5663-77. [PMID: 23106611 DOI: 10.1021/pr300471y] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Vaccination is an effective strategy to reduce the loss of chickens in the poultry industry caused by Marek's Disease (MD), an avian lymphoproliferative disease. The vaccines currently used are from attenuated serotype 1 Marek's disease virus (MDV) or naturally nononcogenic MDV strains. To prepare for future immunity breaks, functional genomic and proteomic studies have been used to better understand the underlying mechanisms of MDV pathogenicity and the effects induced by the vaccine viruses. In this study, a combined approach of quantitative GeLC-MSE and qualitative ERLIC/IMAC/LC-MS/MS analysis were used to identify abundance changes of proteins and the variations of phosphorylation status resulting from the perturbations due to infection with an attenuated oncogenic virus strain (Md11/75C) and several nononcogenic virus strains (CVI988, FC126 and 301B) in vitro. Using this combined approach, several signal transduction pathways mapped by the identified proteins were found to be altered at both the level of protein abundance and phosphorylation. On the basis of this study, a kinase-dependent pathway to regulate phosphorylation of 4E-BP1 to modulate assembly of the protein translation initiation complex was revealed. The differences of 4E-BP1 phosphorylation patterns as well as the measured abundance changes among several other proteins that regulate host transcriptional and translational activities across the virus strains used in this study provide new insight for future functional and biochemical characterization of specific proteins involved in MDV pathogenesis.
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Affiliation(s)
- Ko-yi Chien
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh North Carolina 27695, United States
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43
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Taking AIM at the Start of Translation. J Mol Biol 2012; 423:473-4. [DOI: 10.1016/j.jmb.2012.08.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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44
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Hinnebusch AG, Lorsch JR. The mechanism of eukaryotic translation initiation: new insights and challenges. Cold Spring Harb Perspect Biol 2012; 4:cshperspect.a011544. [PMID: 22815232 DOI: 10.1101/cshperspect.a011544] [Citation(s) in RCA: 328] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Translation initiation in eukaryotes is a highly regulated and complex stage of gene expression. It requires the action of at least 12 initiation factors, many of which are known to be the targets of regulatory pathways. Here we review our current understanding of the molecular mechanics of eukaryotic translation initiation, focusing on recent breakthroughs from in vitro and in vivo studies. We also identify important unanswered questions that will require new ideas and techniques to solve.
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Affiliation(s)
- Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
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45
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Strunk BS, Novak MN, Young CL, Karbstein K. A translation-like cycle is a quality control checkpoint for maturing 40S ribosome subunits. Cell 2012; 150:111-21. [PMID: 22770215 DOI: 10.1016/j.cell.2012.04.044] [Citation(s) in RCA: 177] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2012] [Revised: 03/26/2012] [Accepted: 04/23/2012] [Indexed: 01/09/2023]
Abstract
Assembly factors (AFs) prevent premature translation initiation on small (40S) ribosomal subunit assembly intermediates by blocking ligand binding. However, it is unclear how AFs are displaced from maturing 40S ribosomes, if or how maturing subunits are assessed for fidelity, and what prevents premature translation initiation once AFs dissociate. Here we show that maturation involves a translation-like cycle whereby the translation factor eIF5B, a GTPase, promotes joining of large (60S) subunits with pre-40S subunits to give 80S-like complexes, which are subsequently disassembled by the termination factor Rli1, an ATPase. The AFs Tsr1 and Rio2 block the mRNA channel and initiator tRNA binding site, and therefore 80S-like ribosomes lack mRNA or initiator tRNA. After Tsr1 and Rio2 dissociate from 80S-like complexes Rli1-directed displacement of 60S subunits allows for translation initiation. This cycle thus provides a functional test of 60S subunit binding and the GTPase site before ribosomes enter the translating pool.
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Affiliation(s)
- Bethany S Strunk
- Department of Cancer Biology, The Scripps Research Institute, Jupiter, FL 33458, USA
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46
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Kang T, Kwon NH, Lee JY, Park MC, Kang E, Kim HH, Kang TJ, Kim S. AIMP3/p18 controls translational initiation by mediating the delivery of charged initiator tRNA to initiation complex. J Mol Biol 2012; 423:475-81. [PMID: 22867704 DOI: 10.1016/j.jmb.2012.07.020] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Revised: 07/11/2012] [Accepted: 07/17/2012] [Indexed: 11/28/2022]
Abstract
Aminoacyl-tRNA synthetase-interacting multifunctional proteins (AIMPs) are nonenzymatic scaffolding proteins that comprise multisynthetase complex (MSC) with nine aminoacyl-tRNA synthetases in higher eukaryotes. Among the three AIMPs, AIMP3/p18 is strongly anchored to methionyl-tRNA synthetase (MRS) in the MSC. MRS attaches methionine (Met) to initiator tRNA (tRNA(i)(Met)) and plays an important role in translation initiation. It is known that AIMP3 is dispatched to nucleus or nuclear membrane to induce DNA damage response or senescence; however, the role of AIMP3 in translation as a component of MSC and the meaning of its interaction with MRS are still unclear. Herein, we observed that AIMP3 specifically interacted with Met-tRNA(i)(Met)in vitro, while it showed little or reduced interaction with unacylated or lysine-charged tRNA(i)(Met). In addition, AIMP3 discriminates Met-tRNA(i)(Met) from Met-charged elongator tRNA based on filter-binding assay. Pull-down assay revealed that AIMP3 and MRS had noncompetitive interaction with eukaryotic initiation factor 2 (eIF2) γ subunit (eIF2γ), which is in charge of binding with Met-tRNA(i)(Met) for the delivery of Met-tRNA(i)(Met) to ribosome. AIMP3 recruited active eIF2γ to the MRS-AIMP3 complex, and the level of Met-tRNA(i)(Met) bound to eIF2 complex was reduced by AIMP3 knockdown resulting in reduced protein synthesis. All these results suggested the novel function of AIMP3 as a critical mediator of Met-tRNA(i)(Met) transfer from MRS to eIF2 complex for the accurate and efficient translation initiation.
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Affiliation(s)
- Taehee Kang
- Medicinal Bioconvergence Research Center, Seoul National University, Seoul 151-742, Korea
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47
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Karásková M, Gunišová S, Herrmannová A, Wagner S, Munzarová V, Valášek LS. Functional characterization of the role of the N-terminal domain of the c/Nip1 subunit of eukaryotic initiation factor 3 (eIF3) in AUG recognition. J Biol Chem 2012; 287:28420-34. [PMID: 22718758 PMCID: PMC3436577 DOI: 10.1074/jbc.m112.386656] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
In eukaryotes, for a protein to be synthesized, the 40 S subunit has to first scan the 5′-UTR of the mRNA until it has encountered the AUG start codon. Several initiation factors that ensure high fidelity of AUG recognition were identified previously, including eIF1A, eIF1, eIF2, and eIF5. In addition, eIF3 was proposed to coordinate their functions in this process as well as to promote their initial binding to 40 S subunits. Here we subjected several previously identified segments of the N-terminal domain (NTD) of the eIF3c/Nip1 subunit, which mediates eIF3 binding to eIF1 and eIF5, to semirandom mutagenesis to investigate the molecular mechanism of eIF3 involvement in these reactions. Three major classes of mutant substitutions or internal deletions were isolated that affect either the assembly of preinitiation complexes (PICs), scanning for AUG, or both. We show that eIF5 binds to the extreme c/Nip1-NTD (residues 1–45) and that impairing this interaction predominantly affects the PIC formation. eIF1 interacts with the region (60–137) that immediately follows, and altering this contact deregulates AUG recognition. Together, our data indicate that binding of eIF1 to the c/Nip1-NTD is equally important for its initial recruitment to PICs and for its proper functioning in selecting the translational start site.
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Affiliation(s)
- Martina Karásková
- Laboratory of Regulation of Gene Expression, Institute of Microbiology Academy of Sciences of the Czech Republic, Videnska 1083, Prague 4, 142 20, the Czech Republic
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48
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Aitken CE, Lorsch JR. A mechanistic overview of translation initiation in eukaryotes. Nat Struct Mol Biol 2012; 19:568-76. [PMID: 22664984 DOI: 10.1038/nsmb.2303] [Citation(s) in RCA: 286] [Impact Index Per Article: 23.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Translation initiation in eukaryotes is a complex and highly regulated process requiring the action of at least 12 protein factors. The pathway is distinguished by the formation of a pre-initiation complex that recruits the 5' end of the mRNA and scans along it to locate the start codon. During the past decade, a combination of genetics, biochemistry and structural studies has begun to illuminate key molecular events in this critical phase of gene expression. Here, we outline our current understanding of eukaryotic translation initiation and discuss important outstanding challenges.
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Affiliation(s)
- Colin Echeverría Aitken
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
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49
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Schmitt E, Panvert M, Lazennec-Schurdevin C, Coureux PD, Perez J, Thompson A, Mechulam Y. Structure of the ternary initiation complex aIF2-GDPNP-methionylated initiator tRNA. Nat Struct Mol Biol 2012; 19:450-4. [PMID: 22447243 DOI: 10.1038/nsmb.2259] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2011] [Accepted: 02/07/2012] [Indexed: 01/09/2023]
Abstract
Eukaryotic and archaeal translation initiation factor 2 (e/aIF2) is a heterotrimeric GTPase that has a crucial role in the selection of the correct start codon on messenger RNA. We report the 5-Å resolution crystal structure of the ternary complex formed by archaeal aIF2 from Sulfolobus solfataricus, the GTP analog GDPNP and methionylated initiator tRNA. The 3D model is further supported by solution studies using small-angle X-ray scattering. The tRNA is bound by the α and γ subunits of aIF2. Contacts involve the elbow of the tRNA and the minor groove of the acceptor stem, but not the T-stem minor groove. We conclude that despite considerable structural homology between the core γ subunit of aIF2 and the elongation factor EF1A, these two G proteins of the translation apparatus use very different tRNA-binding strategies.
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Affiliation(s)
- Emmanuelle Schmitt
- Laboratoire de Biochimie, Unité mixte de Recherche 7654, Ecole Polytechnique, Centre National de la Recherche Scientifique, Palaiseau, France.
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